A nuclear fuel assembly for pressurized water reactor (PWR) comprises a bundle of fuel rods and a structure, the structure comprising a lower nozzle, an upper nozzle, a plurality of guide tubes connecting the nozzles and supporting grids distributed along the guide tubes between the nozzles, the fuel rods being supported by the grids between the nozzles.
The guide tubes are generally connected to the lower nozzle by connection devices of the above-mentioned type, the bore being provided in the nozzle and the screw being engaged through the bore in the nut provided at the lower end of a guide tube.
In one conventional embodiment, the screw head has an upstanding annular wall which extends contiguous with the bore once the screw is torqued to its tightened position. Opposite diametric portions of the annular wall on the screw head are then bulged into recesses provided in the bore, thus providing a locking device which prevents self-unscrewing of the screw.
U.S. Pat. No. 4,668,469 describes a connection device of the above-mentioned type comprising an annular locking sleeve which surrounds the head of the screw, the sleeve having a pair of projections engaged in corresponding recesses of the body for locking the sleeve in rotation relative to the body, the sleeve being in frictional engagement with the driving head of the screw for locking the screw in rotation relative to the body.